A digital subscriber line (DSL) technology is a high speed transmission technology that implements data transmission by using a telephone twisted pair, that is, an unshielded twisted pair (UTP), where DSLs include an asymmetrical digital subscriber line (ADSL), a very-high-bit-rate digital subscriber line (VDSL), an integrated services digital network digital subscriber line (IDSL), a single-pair high-bit-rate digital subscriber line (SHDSL)), and the like. The foregoing several digital subscriber lines are referred to as an xDSL below.
Of various digital subscriber line technologies (xDSL), except DSLs using baseband transmission, such as the IDSL and the SHDSL, a DSL using passband transmission allows the DSL and a plain old telephone service (POTS) to coexist in a same twisted pair by using a frequency division multiplexing technology, where the DSL occupies a high frequency band and the POTS occupies a baseband part smaller than 4 kHz.
Generally, each user cable basically includes a plurality of twisted pairs (25 pairs or more), and multiple different services may be run over each twisted pair. Crosstalk occurs between various types of xDSLs when these xDSLs work simultaneously. Performance of some subscriber lines may dramatically decrease due to the crosstalk, and what's worse, when some subscriber lines are relatively long, any DSL service cannot be enabled over these subscriber lines due to the crosstalk.
To reduce line-to-line crosstalk, the prior art provides the following two solutions:
One solution is as follows: After a service is provisioned, a max margin used for activating a line is controlled by collecting a running parameter and by using a max margin (maximum noise margin) algorithm of a dynamic line management (DLM), so that the amount of total sending power can be controlled and the line-to-line crosstalk can be reduced. However, this solution is implemented after the service is provisioned, which does not meet an operation and maintenance habit of a telecom operator. The ideal case should be that all template parameters are determined before the service is provisioned. In this case, quality of the service complies with the requirement after the service is provisioned, and resources and control costs in subsequent optimization should be reduced as many as possible, so as to increase user satisfaction of enabling the service. In addition, the max margin is a level value, which makes the control on the max margin of the line less precise.
The other solution is as follows: After a service is provisioned, a power spectral density (PSD) of the line is calculated by collecting a running parameter and by using a dynamic spectrum management (DSM) L2 algorithm; a sending power spectrum density of the line is controlled by using an optimization algorithm, so that crosstalk impact is imposed as minor as possible on lines in a same cable bundle during working, thereby reducing the line-to-line crosstalk. However, this solution is also implemented after the service is provisioned, which does not meet an operation and maintenance habit of a telecom operator. In addition, the DSM L2 algorithm requires collection of a large amount of data to calculate crosstalk between two lines, and the algorithm is optimized according to a crosstalk channel, which is highly complex. Furthermore, a large amount of data is collected, the operation amount of the algorithm is very large, and an optimization period is very long.
Evidently, how to reduce line-to-line crosstalk during transmission of a digital subscriber line service through spectral planning in the case of service provisioning is a problem that needs to be urgently solved in the prior art.